The present invention is directed to an ink jet printing process. More specifically, the present invention is directed to an ink jet printing process wherein color forming liquids ("inks") are jetted onto a substrate. One embodiment of the present invention is directed to a process which comprises (a) incorporating into an ink jet printing apparatus (1) a developing composition comprising a liquid vehicle and a color developer; (2) an oxidizing composition comprising a liquid vehicle and an oxidizing agent; (3) a coloring composition comprising a liquid vehicle and a dye coupler; and (4) a fixing composition comprising a liquid vehicle and a fixative; (b) causing droplets of the developing composition to be ejected in an imagewise pattern onto the substrate; (c) causing droplets of the oxidizing composition to be ejected in an imagewise pattern onto the substrate; (d) causing droplets of the coloring composition to be ejected in an imagewise pattern onto the substrate; and (e) causing droplets of the fixing composition to be ejected in an imagewise pattern onto the substrate; wherein the process results in at least some portions of the substrate bearing images comprising all four of the developing composition, the oxidizing composition, the coloring composition, and the fixing composition, said portions forming a printed image.
Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
Since drop-on-demand systems require no ink recovery, charging, or deflection, the system is much simpler than the continuous stream type. There are three types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the system's ability to produce high quality copies. Drop-on-demand systems which use piezoelectric devices to expel the droplets also suffer the disadvantage of a slow printing speed.
Another type of drop-on-demand system is known as acoustic ink printing. As is known, an acoustic beam exerts a radiation pressure against objects upon which it impinges. Thus, when an acoustic beam impinges on a free surface (i.e., liquid/air interface) of a pool of liquid from beneath, the radiation pressure which it exerts against the surface of the pool may reach a sufficiently high level to release individual droplets of liquid from the pool, despite the restraining force of surface tension. Focusing the beam on or near the surface of the pool intensifies the radiation pressure it exerts for a given amount of input power. These principles have been applied to prior ink jet and acoustic printing proposals. For example, K. A. Krause, "Focusing Ink Jet Head," IBM Technical Disclosure Bulletin, Vol. 16, No. 4, September 1973, pp. 1168-1170, the disclosure of which is totally incorporated herein by reference, describes an ink jet in which an acoustic beam emanating from a concave surface and confined by a conical aperture was used to propel ink droplets out through a small ejection orifice. Acoustic ink printers typically comprise one or more acoustic radiators for illuminating the free surface of a pool of liquid ink with respective acoustic beams. Each of these beams usually is brought to focus at or near the surface of the reservoir (i.e., the liquid/air interface). Furthermore, printing conventionally is performed by independently modulating the excitation of the acoustic radiators in accordance with the input data samples for the image that is to be printed. This modulation enables the radiation pressure which each of the beams exerts against the free ink surface to make brief, controlled excursions to a sufficiently high pressure level for overcoming the restraining force of surface tension. That, in turn, causes individual droplets of ink to be ejected from the free ink surface on demand at an adequate velocity to cause them to deposit in an image configuration on a nearby recording medium. The acoustic beam may be intensity modulated or focused/defocused to control the ejection timing, or an external source may be used to extract droplets from the acoustically excited liquid on the surface of the pool on demand. Regardless of the timing mechanism employed, the size of the ejected droplets is determined by the waist diameter of the focused acoustic beam. Acoustic ink printing is attractive because it does not require the nozzles or the small ejection orifices which have caused many of the reliability and pixel placement accuracy problems that conventional drop on demand and continuous stream ink jet printers have suffered. The size of the ejection orifice is a critical design parameter of an ink jet because it determines the size of the droplets of ink that the jet ejects. As a result, the size of the ejection orifice cannot be increased, without sacrificing resolution. Acoustic printing has increased intrinsic reliability because there are no nozzles to clog. As will be appreciated, the elimination of the clogged nozzle failure mode is especially relevant to the reliability of large arrays of ink ejectors, such as page width arrays comprising several thousand separate ejectors. Furthermore, small ejection orifices are avoided, so acoustic printing can be performed with a greater variety of inks than conventional ink jet printing, including inks having higher viscosities and inks containing pigments and other particulate components. It has been found that acoustic ink printers embodying printheads comprising acoustically illuminated spherical focusing lenses can print precisely positioned pixels (i.e., picture elements) at resolutions which are sufficient for high quality printing of relatively complex images. It has also has been discovered that the size of the individual pixels printed by such a printer can be varied over a significant range during operation, thereby accommodating, for example, the printing of variably shaded images. Furthermore, the known droplet ejector technology can be adapted to a variety of printhead configurations, including (1) single ejector embodiments for raster scan printing, (2) matrix configured ejector arrays for matrix printing, and (3) several different types of pagewidth ejector arrays, ranging from single row, sparse arrays for hybrid forms of parallel/serial printing to multiple row staggered arrays with individual ejectors for each of the pixel positions or addresses within a pagewidth image field (i.e., single ejector/pixel/line) for ordinary line printing. Inks suitable for acoustic ink jet printing typically are liquid at ambient temperatures (i.e., about 25.degree. C.), but in other embodiments the ink is in a solid state at ambient temperatures and provision is made for liquefying the ink by heating or any other suitable method prior to introduction of the ink into the printhead. Images of two or more colors can be generated by several methods, including by processes wherein a single printhead launches acoustic waves into pools of different colored inks. Further information regarding acoustic ink jet printing apparatus and processes is disclosed in, for example, U.S. Pat. No. 4,308,547, U.S. Pat. No. 4,697,195, U.S. Pat. No. 5,028,937, U.S. Pat. No. 5,041,849, U.S. Pat. No. 4,751,529, U.S. Pat. No. 4,751,530, U.S. Pat. No. 4,751,534, U.S. Pat. No. 4,801,953, and U.S. Pat. No. 4,797,693, the disclosures of each of which are totally incorporated herein by reference. The use of focused acoustic beams to eject droplets of controlled diameter and velocity from a free-liquid surface is also described in J. Appi. Phys., vol. 65, no. 9 (May 1, 1989) and references therein, the disclosure of which is totally incorporated herein by reference.
Still another type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink vehicle (usually water) in the immediate vicinity to vaporize almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability.
The operating sequence of the bubble jet system begins with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble formation or nucleation of around 280.degree. C. Once nucleated, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. This bubble expands until all the heat stored in the ink in excess of the normal boiling point diffuses away or is used to convert liquid to vapor, which removes heat due to heat of vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle, and once the excess heat is removed, the bubble collapses on the resistor. At this point, the resistor is no longer being heated because the current pulse has passed and, concurrently with the bubble collapse, the droplet is propelled at a high rate of speed in a direction towards a recording medium. The resistive layer encounters a severe cavitational force by the collapse of the bubble, which tends to erode it. Subsequently, the ink channel refills by capillary action. This entire bubble formation and collapse sequence occurs in about 10 microseconds. The channel can be refired after 100 to 500 microseconds minimum dwell time to enable the channel to be refilled and to enable the dynamic refilling factors to become somewhat dampened. Thermal ink jet processes are well known and are described in, for example, U.S. Pat. No. 4,601,777, U.S. Pat. No. 4,251,824, U.S. Pat. No. 4,410,899, U.S. Pat. No. 4,412,224, and U.S. Pat. No. 4,532,530, the disclosures of each of which are totally incorporated herein by reference.
U.S. Pat. No. 3,870,435 (Watanabe et al.), the disclosure of which is totally incorporated herein by reference, discloses an almost colorless aqueous ink containing a color coupler which is used to inscribe a record on a recording sheet having a coated layer containing a fine white powder and a color developer which reacts with the color coupler to form a visual record of vivid color of highly durable nature.
U.S. Pat. No. 3,850,649 (Buerkley et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink composition which is particularly suitable for lithographic (wet) offset printing and comprises a quick set vehicle mixed with an iron-complexing agent. The composition provides a storable latent (i.e. invisible or concealed) image when printed on a properly selected low iron-content paper. Treatment of the printed latent image with an iron salt develops the image and makes it clearly visible. Visible material can be printed with the latent material on the same paper using a conventional 2-color offset press.
U.S. Pat. No. 5,443,629 (Saville et al.), the disclosure of which is totally incorporated herein by reference, discloses a latent image ink particularly for use in printing forms such as games or coloring books. An offset lithographic press is used for imprinting a substantially invisible image on a sheet of standard paper. The latent ink used to form the latent image is a mixture of potassium ferrocyanide or other suitable color fixing iron complexing compounds, white ink, and varnish. A developing solution such as ferric chloride or ammonium sulfate is subsequently added to the paper to render the image visible.
Japanese Patent Publication JP 77049366 B, the disclosure of which is totally incorporated herein by reference, discloses a recording system which comprises a pen which applies a colorless ink containing a color developer such as potassium ferrocyanide and a hygroscopic compound such as glycerol dissolved in water to a paper coated with a white mineral powder and a colorless compound such as iron alum which forms color on reacting with the color developer.
Japanese Patent Publication JP 9030107 A, the disclosure of which is totally incorporated herein by reference, discloses a process which includes ejection of droplets of multiple color ink compositions to a recording medium having an absorbing layer for coloring agents to make the coloring agent in the ink composition adhere to the recording image to form a color image. Each of the coloring agents in the color ink compositions are localized at a specific depth of the absorbing layer for coloring agents, and the coloring agents having different color tone do not mingle at the same depth in the absorbing layer. Improved color reproduction can be achieved when multiple types of coloring agent are printed on the same position.
British Patent Publication GB 1398334, the disclosure of which is totally incorporated herein by reference, discloses a printing ink composition capable of forming latent images which can be rendered visible by reaction with metal salts which comprises (1) at least 40 percent by weight of a color stable, quick set vehicle free of metallic driers and having sufficient tack, viscosity, hydrophobicity, and pigment carrying capacity for use in lithographic offset printing, and, dispersed in the vehicle, (2) at least 10 percent of a light colored, solid, particulate water insoluble reactant having an average particle size of 0.5 to 5.0 microns and being capable of forming a strongly colored complex with a coreactant iron salt. The composition is particularly useful for the printing of educational aids such as self-answering examination sheets.
German Patent Publication DE 2505077, the disclosure of which is totally incorporated herein by reference, discloses a water borne writing or printing liquid for producing an invisible recording which contains a mixture of gallic acid and alkali gallate which will react with heavy metal salts.
"Leuco Dye System for Ink Jet Printing," W. T. Pimbley, IBM Technical Disclosure Bulletin, Vol. 23, No. 4, p. 1387 (September 1980), the disclosure of which is totally incorporated herein by reference, discloses ink jet printing with improved archival properties by using leuco or vat dyes. The dyes convert to their permanent form when oxidized. The record medium is first coated or impregnated with an oxidizing agent such as acidic materials, such as acidified clays, organic acids, or polymeric phenols. Upon combining with the oxidant, the dyes convert to their permanent form, becoming insoluble and having high tinctorial strength and excellent archival properties, such as waterfastness and lightfastness.
While known compositions and processes are suitable for their intended purposes, a need remains for improved ink jet printing processes. In addition, a need remains for ink jet printing processes which enable generation of photographic quality images on plain paper. Further, a need remains for ink jet printing processes which enable increased color gamut. Additionally, a need remains for ink jet printing processes which enable increased color intensity. There is also need for ink jet printing processes which generate permanent and waterfast images. In addition, there is a need for ink jet printing processes which exhibit desirable throughput speed. Further, there is a need for ink jet printing processes which enable gray level printing without specific regard to drop ejector resolution, wherein near continuous tone or multigray level images can be realized with simple 300 dpi (dots per inch) drop ejectors. Additionally, there is a need for ink jet printing processes which enable the printing of continuous tone pictorial images without specific regard to drop ejector resolution. A need also remains for ink jet printing processes which enable production of variable spot sizes. In addition, a need remains for ink jet printing processes which enable production of high resolution images.